Hi Kao, Lower back pain is usually caused by weak muscles that will then, spasm. I've lived with it all my adult life, but since I discovered the stretching legs out and then bringing knees up to chest and holding there for a minute....repeat a few times, I haven't had the the back spasms, in a long time.

I believe it's shown above, in Cherie's illustration. The back and hip strengthening exercises are also very good. I hope it works as well for you.